1. Field of the Invention
This invention relates to a process for preventing the deposition of solids on a gas inlet nozzle positioned in a fluidized bed of particles. It particularly relates to a method of preventing the presence of stagnant or slow moving particles in the zone of the gas inlet in a bed of particles. More particularly, it relates to preventing the formation of metallic ash deposits on the nozzle inlet which supplies an oxidizing gas to fluidize a bed of carbonaceous solids containing metallic contaminants.
2. Description of the Prior Art
Fluid bed gasification processes in which a solid carbonaceous material is reacted with an oxygen-containing gas, such as, air or oxygen, and/or steam are well-known in the art. Such a gasification process is shown, for example, in U.S. Pat. No. 3,661,543, which is incorporated herein by reference, and in which an oxidizing gas (air or oxygen) and steam are injected into the bottom of a coke gasification zone. In such processes, the gas inlet nozzle is located in the fluid coke bed and conventionally discharges a gas steam upwardly into the bed. Usually, areas of defluidized coke are present between nozzle injection points. When petroleum coke, which contains metallic contaminants, such as, vanadium and nickel components, is gasified by reaction with steam and an oxidizing gas to produce a fuel gas, a metallic ash-rich coke residue builds up near and around the oxidizing gas inlet of the conventional straight tube, upwardly directed, nozzle. Some of this ash subsequently forms a deposit on the surface and tip of the gas inlet nozzle and thereby interferes with the operation of the nozzle. It is believed that the passage of the metallic ash-rich coke particles through the small oxidizing zone near the gas inlet causes some of the metallic components to be converted to metallic oxides, some of which melt at a temperature lower than the temperature at which the gasification zone is maintained. This molten material readily adheres to the surface and tip of the gas inlet nozzle, solidifies and clogs the orifice of the nozzle.
It has now been found that the presence of stagnant or slow moving particles near the oxidizing gas inlet nozzle and the consequent formation of a solid deposition on the nozzle can be minimized or prevented when the oxidizing gas which also serves as fluidizing gas is injected into a bed of particles in a downward direction at a specified angle and at a given gas exit velocity from the nozzle.